Spatial analysis of karst conduit networks and determination of parameters controlling the speleogenesis along preferential lithostratigraphic horizons

The main objective of this thesis is to improve the understanding of the position and characteristics of karst conduits within a rock massif. Such a characterisation is an important issue in civil engineering and in hydrogeology. Today in practice dissolution voids are considered as random in most cases. However, it is obvious for karst researchers that dissolution void distribution is not random, but defined by parameters controlling the speleogenesis. We developed a method to analyse the 3D geometry of cave systems in order to demonstrate from a statistical point of view that karst conduits position is not random. The analysis of several among the largest cave systems in the World (more than 1500 km of analysed cave conduits) confirmed for the first time quantitatively that the development and position of karst conduits under phreatic conditions is strongly related to a restricted number of so called inception horizons. An inception horizon – a concept introduced by Lowe (1992) – is a part of a lithostratigraphic succession that is particularly susceptible to the effects of the earliest cave forming processes by virtue of physical, lithological or chemical deviation from the predominant carbonate facies within the formation. We demonstrate that probably less than 10 % of the existing bedding partings of a limestone sequence are inception horizons and guide more than 70 % of the phreatic conduits. Our analysis clearly confirms that the influence of these horizons onto the 3D geometry of cave systems is high. Based on the 3D analysis of cave systems as well as on field verifications, 18 inception horizons in six cave systems have been selected for field characterisation and sampling in order to identify the properties and processes that makes these particular lithostratigraphic horizons favourable to karstification. Around 200 rock samples from the horizons and the surrounding rock mass have been analysed. The results evidence that inception horizons have a thickness of some centimetres to decimetres and that it is possible to distinguish between 3 types of inception horizons: Inception horizons where the cave inception took place within the inception horizon (type 1); characterized by a slightly higher primary permeability, pyrite and quartz contents and lower matrix contents than the surrounding rock mass. Usually, fractures propagate through or occur within these horizons. Inception horizons where the cave inception took place at the contact with the inception horizon (type 2); characterized by a lower primary permeability and carbonate contents, but higher pyrite contents than the surrounding rock mass. Fractures usually are ending at these horizons. Inception horizons where the cave inception took place along bedding plane fractures (type 3); already a slippage of just a few millimetres, striation, brecciation and surface irregularities enhance openings along the sliding plane and cause a significant increase in permeability. Furthermore it can be assumed that for the inception of horizons of type 1 the primary permeability will be the relevant factor at beginning of karstification, whereas both the matrix and the pyrite contents are the key factors during the later phases of cave inception and gestation. Whereas for further cave development the total carbonate content will be crucial. For inception horizons of type 2, we can assume that the low primary permeability, the clogging of the pores by the clay minerals, the high content of pyrite (production of aggressive solutions within the horizon that concentrates the dissolution along the contact to the surrounding rock) and the ending of the fractures at the horizon are responsible for the enhanced karstification at the contact during cave inception and gestation phases. Using simple hydrogeological numerical modelling we show that an epigenic karstic rock massif can be subdivided into four speleogenetic zones: 1) vadose cave development zone above the water table, 2) the phreatic cave development and 3) gestation zone within the first tens of metres of the phreatic zone and 4) below them the inception zone. Each of these zones is characterized by typical speleogenetic processes as well as dissolution void distribution. Further, it was possible to explain and reproduce schematically the 3D pattern of different cave systems by using the position and orientation of the inception horizons and the history of the landscape evolution (i.e. the re- and discharge area). This forward analysis provides a first idea of the geometry of the conduits as well as a better understanding of the development of a karst system in time and space (vertical section). Finally, we evaluated the feasibility to combine the improved inception horizon hypothesis, to predict inception horizons, with other current applied methods to improve the prediction of dissolution voids. Furthermore, we proposed a scientific based risk assessment for underground engineering proposes. Essentially, it is now evidenced that it is possible to quantify the probability of karst occurrences inside a karst massif by reconstructing the hydrogeolgical history and identifying the few inception horizons that guide the karstification at a regional scale.

Evidence of inception horizons in karst conduit networks

Marco Filipponi, Pierre-Yves Jeannin, Laurent Tacher

This paper outlines the conclusion from an analysis of 18 large cave systems around the world, comprising more than 1500 km of conduits. The 3D geometry of complex cave systems have been analysed in relation to their geological context as well as their hydrogeological boundary conditions. The methodology allowed for the first time statistical evidence of the inception horizon concept. Thereby it confirms that the development of karst conduits under phreatic conditions is strongly related to a restricted number of so called inception horizons. An inception horizon is a part of a rock succession that is particularly susceptible to the development of karst conduits because of physical, lithological or chemical deviation from the predominant carbonate facies within the limestone sequence. It passively or actively favours the localisation of dissolutional voids.

2008

Typologie géochimique des eaux des aquifères carbonatés des chaînes alpines d'Europe centrale et méridionale

This study describes the spatial heterogeneousness of the chemical composition of underground waters, particularly the trace elements, and the carbon-13 isotope in several carbonate aquifers of the alpine belt in Europe. The research forms part of the AQUITYP project which have been worked on the last 14 years by the Geology laboratory of the Swiss Federal Institute of Technology in Lausanne (GEOLEP). The main aim of the project is to define the typology of the aquifers, based on the chemical characterisation of underground waters. The carbonate aquifers has been divided in several groups chosen after geological, geographical and hydrological criterias. The geological criterias are petrography and depositional environments of carbonates. The geographical criteria is the altitude of the catchment area. The criteria hydrology is the type of flow in karstic systems. The first stage of this research consisted of a selection of 87 carbonate aquifers divided in 13 regions of study in the alpine belt between France and Greece. Aquifers were selected in order to guarantee the absence of external contamination in groundwaters. Sampling were carried out in a period of base-flow, when groundwaters are equilibrated with rocks. The analyse of 112 samples of water provided the basis of the observations of the various chemical and isotopic composition of groundwaters of carbonate aquifers. Lixiviation of rocks forming aquifers provides information about geogenic origin of some trace elements. The geological and hydrogeological context of aquifers The aquifers studied are composed of platform and basin limestones, that form part of the paleogeographic domain of the Tethys. One example of Devonian limestone belongs to the complex of the Palaeozoic of Graz is also included. Each aquifer has homogenous petrographic composition, but from one aquifer to another the petrographic composition may differ. In this research are included pure limestones, marly limestones and dolomites. From a hydrogeological point of view the 87 aquifers show different degrees of karstification, they are placed either in regions of mountains (caracterised by an important hydraulic gradient), either in region of plateau. The surface of the catchment areas is variable between ten km2 (for example the karstic plateau in Slovenia) and a few km2 (for example the Parmelan massif from subalpine belt in France). Discharges of springs are also variable, between 1 and 1000 l/s. The chemical characterisation of water The study of the chemical typology of the waters of carbonate aquifers are carried out on non thermal water rich in oxygen (median values: temperature 8.8°C, dissolved oxygen 11.8 mg/l, Eh 0.4 V, pH 7.2). The total dissolved solids differs between 100 and 600 mg/l. Underground waters are calcium bicarbonate type. Within these facies in some cases, the Mg and S04 content can be superior, thus defining two sub-facies. The iodine content in the groundwaters of carbonate aquifers usually shows higher values than the other types of aquifers of the project AQUITYP. Concentration in the groundwaters of carbonate aquifers is variable between 10 and 60 µg/l. The origin of iodine is caused by the oxidation of fossil organic matter present in the carbonate rocks. Trace elements allows to distinguish groups of aquifers composed of pure limestones, dolomite or deep sea limestones : pure limestones. The aquifers composed of pure limestones are marked by a very small concentration of trace elements. This can be explained by the poorness of the detrital materials (clays, Fe-Mn oxides, heavy minerals) and the compact lithology that reduces the surface of water-rock interaction. dolomite. The typical elements of dolomite aquifers are Mg, U and Mo. The high primary porosity and the brittle deformation of this type of rock favorise a better water rock interaction compared to poor reef limestone aquifers. Examples of this group of aquifers have been selected in the Italian Dolomites and in the Zone of Karavanke in Slovenia deep sea limestones. The barium is a geogenic tracer in some aquifers composed of basin limestones. The aquifers of the Maiolica and of the Scaglia in the Apennine and the Malm aquifer (spring of Grandchamp) in the Prealpes in Switzerland have a high level of Ba in groundwater (between 60 and 220 µg/l). The limiting factor of Ba mobility in this carbonate environment is the concentration of SO42- in the water. The SO42- makes the Ba precipitate in shape of barytes. This process explains the presence of barytes in fractures found in the aquifer of the Calcare Massiccio in the Apennines. The content of carbonate-13 in groundwaters allows to make a distinction between waters infiltrated in catchment areas with or without vegetation and soils. This isotope is also interpreted as a tracer of the type of underground flow in Karstic system (rapid flow in Karstic channels or slow flow in little fractures of the rock). For the project an example has been taken in Tanneben karst, in Austria. This karst shows that water with a slow flow from blocks has a higher 13C content in comparison with fast flow channel water. Finally some analysis of waters from the bottom of soils on the Jura belt in Switzerland showed that during little rain periods the content of isotope is comparable to the one of slow flow waters of the unsaturated zone in the karst. This demonstrate that the isotopic exchange with rock is completed at low horizon in the soil. The vanadium is a geogenic tracer in the Malm aquifer of the Jura belt in Switzerland and in the Cretaceous aquifer in the region of Trieste, in Italy. The origin of vanadium differs in these two examples. In the Jura belt the vanadium comes probably from marly layers of limestones of the low Portlandien. In the region of Trieste the element vanadium is present in bituminous carbonate sediments from inner platform (Calcari bituminosi from Paleocene). In conclusion the importance and the limits of the chemical criterion for the typology of aquifers are shown. This method of distinction of groups of limestone aquifers is one of the tools which permit the determination of the origin of water sources, particularly in underground and borehole construction projects.

EPFL1995

Modeling and Simulation of Energy Efficient Milling Process Plans for Prismatic Parts

Nenad Nesic

The milling process has been continuously optimized from many aspects: forces, velocities, stability, quality. Numerous papers have been published that report results in the domain of toolpath optimization with criteria such as raising the quality of the machined part, obtaining a stable machining process and maximizing the material removal rate. However, only recently researchers have started investigating the ecological impact of machining processes. With the constantly increasing prices of electrical energy and all environmental problems caused by the production and waste of the energy, it has become indispensable to look for ways to optimize machining processes from the energy consumption aspect, too. It is in this domain, then, that the work described in this dissertation contributes – to add a new criterion for the sustainable operation of machine tools: reducing the energy consumption during the use phase of the machine tool. The total energy spent in a machining process is the sum of power spent by all machine tool subsystems multiplied by the time that they are working. Therefore, the operating strategies for increasing energy efficiency for the high-speed machining processes must be oriented towards the reduction of the total machining time (productive and unproductive) and reduction of instantaneous consumed power in the machining process or, preferably, both. There are many causes for milling process time and energy inefficiency. The major sources of potential time reductions include: (i) the issues related to the geometry and topology of the toolpath („air-time”, overlapping segments, gouge and uncut regions, orientation of the toolpath), (ii) the issues related to the kinematics of the feed drives (the feed velocity/acceleration profile). The possible domains for power consumption reduction are related to the forces that exist in the machining process (cutting, inertial, gravitational and friction forces). The power invested to overcome the cutting force is necessary for the machining process but its consumption should be optimized through constant cutting engagement and feedrate scheduling strategies. The other forces are responsible for the pure mechanical power loss and they should be minimized. The optimization variables for inertial and gravitational forces include the feed motion profile and moving mass configuration, while friction losses are load and/or velocity dependent. In addition, there are some power losses in the electric components of machine tool drives (electrical power losses), whose dependency on velocity and mechanical load can also be modeled. Despite many research efforts to analyze and model the phenomena causing inefficiency of the machining process, they are usually not taken into account during milling process planning. In fact, rare are the attempts to use this knowledge to optimize the milling process with more than one of the above mentioned criteria. The reason for that lies in the fact that increasing the instantaneous values of tool engagement and feedrate in order to minimize total machining time also increases the consumed power and, indirectly, deteriorates the tool and/or destabilizes the cutting process. The existence of conflicting criteria in the objective functions imposes the use of evolutionary algorithms for multiobjective optimization. The process of experimental validation of such an optimization model requires costly and complex external hardware setup and it is also time consuming. Hence, there is an emerging need for the development of an accurate model, which would be used for the simulation of the milling process and testing the competing optimization strategies. The ultimate goal of contemporary manufacturing science and engineering is the development of a holistic virtual machine tool system. The motivation of this PhD research is to contribute to this objective by developing the “virtual milling process for prismatic parts (produced by 2.5D milling)”. This category of objects is selected, because the majority of CNC milling tasks can be performed using 2.5D milling. A very large number of mechanical parts are prismatic (their geometry consists exclusively of features that represent 2D contours extruded in a perpendicular direction). Parts that are even more complex are usually produced from a blank by a 2.5D roughing and 3D–5D finishing. Therefore, development of an accurate model of a 2.5D milling process represents a significant contribution to manufacturing engineering. Starting with above given problem description, we have defined the following research objectives: 1. Model power and energy consumption of a 2.5D milling machine as a function of the toolpath geometry (curvature and continuity), cutting engagement, real feedrate profiles and spindle rotational speed, taking into account moving mass configuration, all power losses (mechanical and electrical) in feed-axis and spindle drives and electromechanical constraints of servo drives; 2. Design an integrated software environment for simulation of the developed models; 3. Validate the model experimentally; 4. Demonstrate the potential of its use for multi-objective process optimization. Cutting engagement calculation is performed by using two competing methodologies, in order to make a comparison of their performances. The first one, the pixel based method, is based on discrete image processing, while the other, the exact method, is based on Boolean operations and vector geometry. The tests performed in more than 20 feature/toolpath combinations demonstrate that the exact method is more precise whereas the pixel-based method is computationally much faster. The machine tool operator commands a constant feedrate value. During the process, based on his/her subjective judgment, he/she can manually tune it to keep the process in the desired boundaries. One of the objectives of this research is to predict the real feedrate values so that they can be integrated in the part program before the process start. The feasible profiles of feed velocities for each toolpath segment are analyzed by answering the following questions: can the commanded feedrate be achieved and with what sequence of acceleration and deceleration phases, how much the tool has to slow down in corners and how does the feedrate profile degenerate in segments where the commanded feedrate cannot be reached? In order to determine all forces and torques, a machine tool model is developed. The following subsystems are modeled as rigid bodies (without vibrations): feed motor shaft, transmission, lead screw/nut pair, lead screw bearings, guides (sliding and rolling design), table with the workpiece and electrospindle (rotor, stator and bearings). All kinetic variables (linear and angular speeds; cutting, inertial and friction forces and torques) are then calculated in the joints of this multi-body system. The modeling of all speeds, forces and torques that occur in the machine tool system during the machining process, allows for calculation of various indicators of process time and energy efficiency: material removal rate, total machining time, useful power (invested in cutting), power loss due to the friction in the joints, power losses in electrical motors, electrical energy consumption of feed and spindle drives. In order to assess the accuracy and the reliability of the developed model two sets of experiments have been performed. The model validation is performed on several subsystem levels and the simulation results show a very good compliance with the experimental results. The first experimental setup consists of the force dynamometer, to measure cutting force components in linear axis directions, two laser optical position sensors, to measure the real feedrate and the power sensor, to measure the total power consumption of the machine tool electrical motors. The machining process was performed on the 6-axis machining center C.B. Ferrari A152 and the data acquisition platform was developed in LabVIEW 2010. The second experimental setup consists of the torque dynamometer, to measure the cutting torque directly on the spindle, the built-in current sensor that measures the motor current proportional to the electrical power consumed by the spindle and, again, the power sensor, to measure the total power consumption of the machine tool electrical motors. This time, MIKRON HPM 600U, a 5-axis milling machine equipped with the controller iTNC530, was used for the experimentation. The developed model is ready for practical implementation. Several examples have been prepared to demonstrate its capabilities in the domains of milling process simulation, sensitivity analysis and prospective optimization strategies. These examples include the prediction of various kinetostatic variables for given toolpaths, choice of the optimum machining strategy (minimization of machining time, moving mass and energy consumption) and process optimization by feedrate scheduling (reduction of cutting force fluctuation). As a conclusion, the major contribution of this PhD research is the development of a comprehensive rigid-body dynamics model of a machine tool system, aimed for the generation, simulation and optimization of 21⁄2D milling process plans. The model features several novelties compared to existing approaches: (i) it takes into account the machine tool rigid body dynamics and real tool kinematics in toolpath planning, (ii) it predicts all mechanical and electrical power losses in the machine tool system (iii) it allows the modeling of machine tool system electromechanical constraints. The model was experimentally validated on two real machine tools in different workshops and its capabilities for the simulation of different toolpath patterns and optimization of process parameters were successfully demonstrated using several examples.

EPFL2012

Modeling and Simulation of Energy Efficient Milling Process Plans for Prismatic Parts

Nenad Nesic

EPFL2012

Typologie géochimique des eaux des aquifères carbonatés des chaînes alpines d'Europe centrale et méridionale

EPFL1995